1. Field of the Invention
This invention relates to laboratory equipment, and more particularly to a pipette dispensing block used in biologically-related laboratories that aspirates and dispenses fluid volumes in a precise and controlled manner.
2. Description of the Related Art
Recently, biology has increasingly incorporated elements of basic molecular and atomic chemistry, yielding the field of biotechnology. The secrets nature has hidden in mammalian and other biology are increasingly being unraveled and discovered. With greater knowledge of molecular biochemistry, genefic structure and effect, coupled with the ability to reproduce biologically active molecules quickly and easily, a corresponding increase in research has demanded tools and equipment that are able to promote the investigative activities related to present day biotechnology.
U.S. Pat. No. 5,525,302 issued Jun. 11, 1996 to Astle for a Method and Device for Simultaneously Transferring Plural Samples sets forth machinery by which standard samples in a standard sample container can be transferred, aspirated, and dispensed in a highly-controlled manner. The Astle '302 patent is incorporated herein by this reference hereto.
In the Astle '302 patent, a pipette system (particularly that one which is shown in FIGS. 1B and 5 of the Astle '302 patent) is disclosed relating to the construction and operation of a pipette system. As shown in FIG. 5, internal and external reservoirs may serve to control fluid flow through the hollow tube piston 50 when the clamp mechanism 140 is opened by separating the rod 146 from the anvil 142.
In the Astle '302 patent, the lift plate 52 controls the relative position of the hollow tube piston 50 in its travel inside the cylindrical channel 60. The elastomeric O-ring 62 seals the cylindrical channel 60 so that a vacuum may be pulled on the pipette tip 70, thereby allowing it to aspirate or, conversely, dispense fluid.
Note should be taken that if the elastomeric O-ring 62 breaks down through wear or otherwise does not seal the cylindrical channel 60, gases such as air can flow into the cylindrical channel 60 and thereby defeat the vacuum pulled on the cylindrical channel 60 by the motion of the lift plate 52 and the hollow tube piston 50. The same is similarly true when pressure is applied via the piston 50.
Consequently, it can be seen that the elastomeric O-ring 62 is a weak link in the Astle '302 patent system. This weak link is known in the art and is currently addressed by the application of grease, oil, or the like adjacent the elastomeric O-ring 62 as it suffers wear, tear, abrasion, and deterioration throughout the useful life of the elastomeric O-ring 62.
The opposite end of the cylindrical channel 60 is sealed by the pipette tip 70 and a second sealing O-ring 66 in conjunction with the hollow cylindrical pin extension 64. FIG. 5 of the Astle '302 patent shows all these features.
Additionally, FIG. 5 of the Astle '302 patent shows the use of retaining rings 54, 56 of the upper and lower portions of the top end of the hollow tube piston 50. As the hollow tube piston 50 forms one of ninety-six (96) such hollow tube pistons in an 8.times.12 array of such pistons, it becomes a daunting, time-consuming, and tedious task to replace one or several of the hollow tube pistons 50. Additionally, in order to remove one single piston such as a central one of the hollow tube pistons 50, the entire lift plate 52 may be required to be lifted up and away from the head block 40. This causes each and every one of the hollow tube pistons 50 to be disengaged from the head block 40, breaking the seal formed in conjunction with the elastomeric O-ring seal 62. The retaining rings 54, 56 consequently limit the utility of the Astle '302 patent device by making access to individual pistons more difficult.
Consequently, it can be seen that the use of retaining rings (such as those indicated by reference numbers 54 and 56, and the Astle '302 patent) creates some drawbacks with respect to the useful life and easy repair of pipette systems such as that shown in the Astle '302 patent.
Other developments in the pipette dispensing art are known and are indicated in summary fashion below.
U.S. Pat. No. 4,087,248 issued to Miles on May 2, 1978 for a Multiple Assay Machine and Method has a motor-driven housing and a syringe battery. An upper platform is mounted on threaded bolts so as to be capable of vertical movement with the turning of the bolts. A retaining syringe plunger plate is secured to an upper platform. The syringe battery has a rectangular housing with an upper guide plate mounted on a housing ceiling having a plurality of channels for guiding plungers. The syringe plunger plate has a hollow center for receiving the plunger heads and holding them in a fixed position. To perform an immunoassay, the syringe battery is introduced into the motor driven housing by sliding the syringe plunger plate between the L-shaped arms of the upper platform.
U.S. Pat. No. 4,106,911 issued to Marcelli on Aug. 15, 1978 for a Device for Examining a Plurality of Microdoses of Liquid is a dispenser of micro-doses of liquids having a base plate with a frame having a vertical arm. A motor is provided with a vertical screw arranged to position a slide block having an extension in the form of a horizontal plate with which the ends of plunger rods of syringes are made fast by means of clips. The bodies of the syringes are made fast with a support. When the motor is running, it moves a nut along a screw and varies the distance between a plate (indicated by reference number 11) and a support, thus enabling the plunger rods to move inside the bodies of all the syringes.
U.S. Pat. No. 4,602,517 issued to Schultz on Jul. 29, 1986 for a Fluid Sampling Method and Apparatus contains a multiple syringe dispenser having a central block assembly, an actuator assembly, and a syringe clamp assembly. Block members of the clamping assembly have protective frictional pads affixed to the V-shaped slots to delicately grip the handles of syringe tubes. The block and actuator assembly provides for the intermittent moving of a drive rod that raises a syringe plunger support assembly having lower and upper plates. Slots in the lower plate allow the insertion of a plunger member whereby the enlarged disk-like ends of the plungers are held by a cushioning pad extending the length of the upper and lower plates. Plungers fit into a cylinder of the syringe and the plungers can all be raised or lowered simultaneously by means of the actuator. A thermally-releasable sample collecting device has an absorber tube with its small diameter front end supported by a locating collar having two (2) O-ring seals. A rearward locating collar has O-ring seals for supporting the larger diameter rear end portion of the absorber tube.
U.S. Pat. No. 5,497,670 issued to Carl on Mar. 12, 1996 for a Liquid Dispensing Apparatus Including Means for Loading Pipette Tips onto Liquid Dispensing Cylinders and Maintaining the Loading Force During the Apparatus Operation Cycle is directed to an apparatus for dispensing controlled amounts of liquid into receptacles. The apparatus has a plurality of plate members either fixed or movable for supporting and dispensing liquids through disposable pipette tips. Fixed cylinders and a cylinder plate are attached to a cylinder mounting plate fixed to shafts. Pistons move in a vertical direction within the fixed cylinders. Each piston passes through a Teflon.RTM. seal. The pistons are connected to a piston plate using a ball and socket mechanism to provide accurate alignment. Each piston is allowed to swivel from the center point of the ball joint. The ball ends of the pistons are attached to a movable piston plate. The piston and cylinder assembly can be removed from the apparatus with the piston plate fixed to a larger plate that slides up and down along the shafts.
Despite the foregoing development and advances in the pipette dispensing art, it remains a problem in the art, solved by the present invention, to maintain a proper vacuum seal for sliding pipette pistons as well as providing convenient and well-engineered components by which a lifting plate for such pipette pistons can have such pistons easily mounted and dismounted (attached and detached) to it.